You can call RunasSpc directly like the following command
runasspc.exe /program:"c:\windows\system32\regedt32.exe" /user:"admin"
/password:"pass" /quiet
There is no security check and the password is in cleartext.

If you want to encrypt the logon account you must configure an
encrypted file
with runasSpc.exe (on commandline) or
runasSpcAdmin.exe (a graphical user interface).
Take a look below on
>>Examples to build an encrypted file<<:

After you have build a encrypted file, you can call the crypt
file with
runasspc.exe
like the following possibilities
A) If the name of the encryptfile is
>>crypt.spc<< you can start it by a
double-click on Runasspc.exe.in the same directory.
B) Drag your crypt file and drop it on Runasspc.exe
C) On command line bypass the startup dialog of Runasspc with option
/quiet
>>
c:\path\runasspc.exe
/cryptfile:"path\NameOfCryptfile.spc" /quiet <<
D) Create a shortcut
>> c:\path\runasspc.exe
/cryptfile:"path\NameOfCryptfile.spc" <<
E) Link the file extension (open with) *.spc on your
system to Runasspc.exe to run the crypt file by
double-click.
You can also use your own file extension

Examples to build
an encrypted file

A)
With command runasspc.exe
You can find samples to build an encrypted file with runasSpc.exe in
the
file readme.txt or call >> runasspc.exe -h
<< to get help